Dominic Zukiewicz's Technical Blog

Monday, 23 December 2013

In the last blog post, I described a solution that was broken down into different areas per location. The MVC project has this structure:

Areas

UK

US

HK

Controllers

Views

Each area had shared UI implementations for the most part, but required specialisation on the business logic side.

Problem

Specialising the services isn’t too much of a problem. You have an interface for the basic functions, and then specialise them within. What made our implementation work difficult is that there were specific repositories for each area! This was because each area interacted with a database of differing schema AND differing platform.

Design

The design of the services is fairly straightforward. You create the interface and then specialise each implementation like this:

So what is the problem? The problem is that there are multiple controllers called OrderSummaryController. They all have the same constructor, which looks identical and does conflict with the base class.

Quick-recap

I'm throwing a lot of code at you at the moment. It is an important lesson to learn about how this solution is working in the bigger scheme of things. We want to use a controller and its base to share functionality. We also want to make sure the signatures match, as it will making unit testing much easier. My solution is attempting to keep the constructors the same signature, so that a) unit testing can be easier and b) so that when a new area is created, just the constructors need copying into the new file.

Ahh - you're back! Ok, so what are we trying to do? We want Autofac to differentiate between a class and its base. You'll find Autofac throws all sorts of resolution errors in this scenario. Luckily, if you don't mind taking the plunge and allowing a litle AutoFac code into your concrete controllers, all is not lost!

This constructor overload gives AutoFac an easy way in. The beauty of it is that the application is still unit testable via the IOrderService and ICurrencyFormatter, but the IComponentContext is giving you an easier (i.e. time-saving) way in. Now, time for the hooking-up within MVC. We need to register that Module, so that MVC resolves items correctly. The easiest (and most common way) is to inherit from the DefaultControllerFactory - the MVC built-in resolver - and register the ServiceInitializationModule. We then re-point MVC at this resolver instead of its default one.

Summary

In this blog, I've described a scenario where an MVC application is separated into areas. Those areas all use different services, due to the business logic being different for them. In addition, the repositories themselves are also different.

Therefore, you should have come away with the following points

A base controller can have multiple implementations in different areas

Areas can have different services being injected into the controllers

The services can even have repositories of differing concrete types injected as well.

This analysis took several weeks to get working. I wasn't able to find it possible with any other framework, but if you do find one that does, let me know!

In the last blog post, I described a solution that was broken down into different areas per location. The MVC project has this structure:

Areas

UK

US

HK

Controllers

Views

Each area had shared UI implementations for the most part, but required specialisation on the business logic side.

Problem

Specialising the services isn’t too much of a problem. You have an interface for the basic functions, and then specialise them within. What made our implementation work difficult is that there were specific repositories for each area! This was because each area interacted with a database of differing schema AND differing platform.

Design

The design of the services is fairly straightforward. You create the interface and then specialise each implementation like this:

So what is the problem? The problem is that there are multiple controllers called OrderSummaryController. They all have the same constructor, which looks identical and does conflict with the base class.

Quick-recap

I'm throwing a lot of code at you at the moment. It is an important lesson to learn about how this solution is working in the bigger scheme of things. We want to use a controller and its base to share functionality. We also want to make sure the signatures match, as it will making unit testing much easier. My solution is attempting to keep the constructors the same signature, so that a) unit testing can be easier and b) so that when a new area is created, just the constructors need copying into the new file.

Ahh - you're back! Ok, so what are we trying to do? We want Autofac to differentiate between a class and its base. You'll find Autofac throws all sorts of resolution errors in this scenario. Luckily, if you don't mind taking the plunge and allowing a litle AutoFac code into your concrete controllers, all is not lost!

This constructor overload gives AutoFac an easy way in. The beauty of it is that the application is still unit testable via the IOrderService and ICurrencyFormatter, but the IComponentContext is giving you an easier (i.e. time-saving) way in. Now, time for the hooking-up within MVC. We need to register that Module, so that MVC resolves items correctly. The easiest (and most common way) is to inherit from the DefaultControllerFactory - the MVC built-in resolver - and register the ServiceInitializationModule. We then re-point MVC at this resolver instead of its default one.

Summary

This is part 1 of a series of blogs, where I aim to give an answer to a question I posted on StackOverflow a while ago. Although the answer was useful, the solution was already implemented and thought it would be best to describe what the problem in more detail.

Problem

Our team were tasked with creating a consistent looking website, which would interact across several different locations. The locations would all be owned by a parent company, who were creating the site. At the project outset, an estimated 70-90% of the UI would look the same. There were caveats to be aware of when developing the site.

Each location used a different order number format

Each location has a custom currency format for the screen. For example;

United Kingdom (2 decimal places) = 1.00 GBP

Hong Kong (4 decimal places) = 1.0000 HKD

United States (3 decimal places) = 1.000 USD

Each location had a different database schema – as these companies were buyouts.

Each location may contain a different database platform.

Each location may (or may not) require customised business rules. A base set of rules would be applicable and customised as such.

Design

The application was divided into 3 parallel sections / areas. The MVC structure of the application looked like this:

Areas

UK

Controllers

Views

US

HK

Controllers

Views

We also had some idea that most of the functionality would be the same, expect for specific UI tweaks. Luckily, the idea of shared functionality became apparent very early on in the project, so we had a starting point to go from.

Solution

We decided to have a base controller to contain a usual-case scenario for a particular process in the shared ~/Controllers directory. Each area would then inherit from this base controller, so that functionality was always available for all areas by default. The only additional work required was when the area needed to specialise the behaviour.

This was a good starting point for us, because we always had out-of-the-box functionality available to us. We only implemented additional functionality when required.

Overriding a view

We also had the additional benefit of having some inside knowledge of the ViewModel coming back, because we knew what service we were calling. This came in handy when the View had to be re-implemented. For example:

Quick re-cap - what have we actually achieved here?

What we have achieved is a shared single controller, that allows customisation when required. By default, all controllers will use the same view. If you wanted to add a significantly different view, you can add it to the area, so that there is a clean separation of concerns. So lets say the UK has a customised branding of the order summary screen - radically different from the default, you can add it to the specific area:

Areas

UK

Controllers

OrderSummaryController

Views

OrderSummary

Index.cshtml

US / HK

Controllers

OrderSummaryController

Controllers

OrderSummaryBaseController

Views

OrderSummary

Index.cshtml

Summary

In this blog post, I demonstrated the use of a shared controllers, whilst allowing customisation between areas when required. This allows a new area to be built *almost* out of the box immediately.

There is a problem with this example; every controller is using a poor mans Dependency Injection. That means when a new area is brought in, every controller needs to be re-implemented.

So in the next blog, I will show you how we tackled this problem, so that new areas need only a little configuration to get up and running.
In this blog, I've described a scenario where an MVC application is separated into areas. Those areas all use different services, due to the business logic being different for them. In addition, the repositories themselves are also different.

Therefore, you should have come away with the following points

A base controller can have multiple implementations in different areas

Areas can have different services being injected into the controllers

The services can even have repositories of differing concrete types injected as well.

This analysis took several weeks to get working. I wasn't able to find it possible with any other framework, but if you do find one that does, let me know!

Monday, 2 April 2012

I’m currently brushing up on my WCF after my exposure to WSE 3.0 a few years ago. In anticipation of upcoming client work and lack of a TS: WCF Application with the .NET Framework 4 book based material (note it is only course-based), I opted for a good solid book that covered the subject matter in a thorough way.

In Chapter 4, “Protecting an Enterprise WCF Service”, he uses some examples where you enter your domain, username and password directly into the code(!). BUT – he does have a warning on every code sample:

Warning: This code is for illustrative purposes in this exercise only. In a production application, you should prompt the user for their name and password. You should never hard-code these details into an application.

Now, I do nearly all of my development on my work laptop. The thought of someone just searching my computer remotely for files with my well-known domain and username puts me off completely. So instead, I decided to apply encryption to it and looked for a way which did not require me to write another program.

Using existing tools to apply the encryption

In the TS: Web Applications with the .NET Framework 4, they discussed how to encrypt the <connectionStrings> section in your web.config. However, I want to leverage this to encrypt my <appSettings> section instead.

First thing, start up a Visual Studio Command Prompt and CD to your location. We want to rename the app.config (prior to the build process) to web.config. For this example, we’ll assume my application in development is at C:\Projects\EncryptConfig directory.

The thing to note here is it is using the DataProtectionConfigurationProvider accesses the Data Protection API which is a user-specific API. It is fine as long as you always log in with your user, on your domain. But if you tried to distribute this application, the section would never be able to be read by another computer.

The RSAProtectedConfigurationProvider allows you to encrypt specific to the user or the machine. It also allows you to export the key so that it can be moved to another machine. This would be useful over a web farm (this is an IIS tool after all), where the <machineKey> can be shared across computers.

In any case, if you are looking to distribute this application and encrypt the contents of a configuration file, be sure you understand what encryption methods are available to you.

Okay, that is pretty horrific. Does the job, no doubt but when it comes to editing this in the application, it is a complete nightmare. It selects single rows, changes their width accidently. When you have a bit of luck actually selecting the outer div, the Code Snippet editor even warns you that it is going to attempt to read it. When viewing this on a mobile device, it looks even worse. Much worse trust me!

At the same time I was catching up with my Google Reader and was looking through posts I'd missed by Scott Hanselman. He was looking for a syntax highlighter for Windows Live Writer a few years ago. He also went to the trouble of writing a Windows Live Writer plug-in for it. But luckily, things have been made much easier.

Tuesday, 27 March 2012

(Apologies for re-posting this – I thought I was deleting a draft post and ended up deleting the actual post!)
I was looking at Stack Overflow today and I saw a question where a user wanted to change the Web.config when the number of Sessions reaches 0. He wasn’t aware of any way to find out the Session Count, or any automated way to do this. I thought I’d have a go anyway using a C# .NET Console Application anyway … but then I discovered PowerShell!

To summarise PowerShell, think of it like a command prompt on steroids! Not only can you do the usual process starting, killing and file system navigation, but it provides a much more streamlined command system. You also have hundreds, if not thousands of commands at your disposal.So let me talk you through how I would have done this in .NET and then the equivalent PowerShell implementation I used.

Goals of the application

Get the Session Count of IIS in total from a performance counter

If Count > 0, quit

Stop IIS

Change web.config

Start IIS

Retrieving performance counters in .NET for the Session Count

I’ve recently passed my TS: Data Applications in the .NET 4 Framework exam, which covered how to create and retrieve performance counter data into your applications. So there’s step one – wait until the Active Session Count is 0. An example of retrieving this is:

These values match up to those in the Performance Monitor (perfmon.exe).

In PowerShell, performance counters are easily retrieved as well. There is a specific command for retrieving them. PowerShell declares variables inline using a $ prefix, so here is how to retrieve the same counter in PowerShell. I saved these to a file called “ChangeIIS.ps1”:

I know what your thinking. How can we access the file in PowerShell? One of the fantastic things with PowerShell is that you have access to all of the .NET classes (including static methods and classes) at your disposal. So here is the same code in PowerShell:

1: # Set values

2: $location = "d:\web.config"

3: $newTimeout = "20"

4:

5: # Open file and change value

6: $doc = new-object System.Xml.XmlDocument

7: $doc.Load($location)

8: $doc.SelectSingleNode("//sessionState").timeout = $newTimeout

9: $doc.Save($location)

Notice how I am using a “timeout” variable directly. PowerShell has exposed the attribute as a property of the .SelectSingleNode() method. How do I know that? Well, if you execute this in isolation, you’ll get a nice helpful output on all of the properties available to use directly:

PS C:\> $doc.SelectSingleNode("//sessionState")

timeout #text

------- -----

20 20

Now we have a PowerShell script in its entirety:

1: # PowerShell script to modify the 'timeout' value in the specified web.config

Granting permissions to the Script

We’re not done yet. PowerShell also has a security feature that doesn’t allow users to just run PowerShell scripts as soon as they are created. They have to come from a credible source to be run straight away.
In order to run this script, we need to tell PowerShell to bypass security checks for this specific process (or user). For security reasons, I will grant access for this process, as we will only want to run this script once.

Open a Command Prompt – Right Click – Properties - "Run As Administrator"

Type powershell.exe

Type Set-ExecutionPolicy –scope Process Bypass

Type sl <directory of file> – sl acts like cd on the command prompt

Type $ ‘.\ChangeIIS.ps1’

And off we go!

Summary

Where opportunities arise to try out new technologies, it is always work having a go. PowerShell isn’t difficult to learn. In fact, its actually very powerful and intuitive. It is also a great ‘Immediate Window’ style interface to try out .NET code. I’m starting to use it quite a lot for even simple calculations:

Monday, 27 February 2012

Today I sat with a colleague and went through how we could implement testing on existing code, without affecting the data in the database. For anyone who answers that question the words “Dependency Injection” – well done! Maybe this post isn’t for you!
But I wanted to give anyone asking themselves this question a short guide on how to get this working, as it is a common problem faced when adapting an existing project to include unit testing.

The problem is now, you’ve wiped the password for that user. If it is hashed in the database, you have no way of retrieving it without modifying it manually. I suppose you could re-apply the original user, but then you are now having to do a tidy up exercise after every test. If another test depends on that user account being valid (e.g. a UI test to log that user in), then you’re going to fail more tests and the problem will only get worse.

Dependency Injection

Dependency Injection allows us to “inject” the database we would like to modify. Some developers like to have their own database that can be freely modified whenever. But in the long term, the maintenance of tidying this database, coupled with the speed of database connections for thousands of tests becomes unmanageable. Ideally, you want these tests to pass as soon as possible so you can get on with your work.

But as this code stands, we will always point at the database. So we’ll need to do some slight modifications to get this code more flexible, without breaking existing code.

Step 1 – Extract an interface

The easiest step is to use Visual Studio to extract an interface for you. You do this by right clicking on the class name of the DataAccess layer > Refactor > Extract Interface

Once you’ve clicked “Select All” and “OK”, this gives you your current code, implementing a newly created interface, which I will rename IRepository (and make public).

Step 2 - Adapt the service layer to accept an IRepository

Next, we adapt the UserService class to accept a new parameter, to allow us to “inject” the database into the class. This way, existing code still works and the test code can take advantage of the new constructor.

Notice I’m using an internal constructor intentionally, as I don’t want to expose this to just anyone. What I can do is instruct the CLR that internals are visible to another assembly. This is done in the AssemblyInfo.cs class for the DataAccess layer like this:

[assembly: InternalsVisibleTo("Tests")]

Note that I have used the Assembly Name of the assembly to which the internal fields, properties, methods and constructors can be accessed.

Step 3 - Inject the new repository

Now, we are able to modify our test to pass in the TestRepository class we created, so that when the UserService is created, it will access our implementation.

Now – okay – the application will throw an exception! Because we haven’t implemented the TestRepository class and left it at its default implemention, the methods will throw errors. But by writing some simple code, which does as much as we need to get going, we no longer rely on running our tests through the DB:

There are frameworks called Mocking frameworks, that can even alleviate you of this burden. But I’ve yet to explore them enough to include in this blog.

Summary

In this blog, we have looked at a common example that many developers face. We have adapted the existing functionality, without breaking existing code, but extending it for use with a testing framework.

This adaptation allows you to concentrate on testing all of those permutations within the UserService, which is what we actually want to test.

I will adapt a full tutorial of this blog, so that users can try out the refactoring for themselves.